Syntheses and evaluation of a homologous series of aza-vesamicol as improved radioiodine-labeled probes for sigma-1 receptor imaging.

Sigma-1 receptor imaging probes for determining the expression levels are desirable for diagnoses of various diseases and companion diagnoses of therapeutic agents targeting the sigma-1 receptor. In this study, we aimed to develop probes with higher affinity for the sigma-1 receptor. For this purpose, we synthesized and evaluated compounds, namely, vesamicol derivatives, in which alkyl chains of varying chain length were introduced between a piperazine ring and a benzene ring. The binding affinity of the vesamicol derivatives for the sigma-1 receptor tended to increase depending on the length of the alkyl chain between the benzene ring and the piperazine ring. The sigma-1 receptor of 2-(4-(3-phenylpropyl)piperazin-1-yl)cyclohexan-1-ol (5) (Ki = 5.8 nM) exhibited the highest binding affinity; therefore, we introduced radioiodine into the benzene ring in 5. The radioiodine labeled probe [125I]2-(4-(3-(4-iodophenyl)propyl)piperazin-1-yl)cyclohexan-1-ol ([125I]10) showed high accumulation in the sigma-1 receptor expressing DU-145 cells both in vitro and in vivo. Co-injection of [125I]10 with an excess level of a sigma receptor ligand, haloperidol, resulted in a significant decrease in the tumor accumulation in vitro and in vivo, indicating sigma receptor-mediated tumor uptake. These results provide useful information for developing sigma-1 receptor imaging probes.

Development of a novel radiobromine-labeled sigma-1 receptor imaging probe.

INTRODUCTION: Sigma-1 receptor is a target for tumor imaging. In a previous study, we synthesized a vesamicol analog, (+)-2-[4-(4-bromophenyl)piperidino]cyclohexanol [(+)-pBrV], with a high affinity for sigma-1 receptor, and synthesized radiobrominated (+)-pBrV. This radiobrominated (+)-pBrV showed high tumor uptake in tumor-bearing mice; however, radioactivity accumulation in normal tissues, such as the liver, was high. We assumed that the accumulation of (+)-pBrV in the non-target tissues was partially derived from its high lipophilicity; therefore, we synthesized and evaluated (+)-4-[1-(2-hydroxycyclohexyl)piperidine-4-yl]-2-bromophenol [(+)-BrV-OH], which is a more hydrophilic compound. Although we aimed to develop a PET tracer using 76Br, in these initial studies, we used 77Br because of its longer half-life. METHODS: (+)-[77Br]BrV-OH was synthesized using the chloramine-T method with a radiochemical purity of 95%. Lipophilicity and affinity for sigma-1 receptor of (+)-[77Br]BrV-OH were determined, and biodistribution experiments were performed. We also performed an in vivo blocking study by co-injecting excess amounts of the sigma-1 receptor ligand, SA4503, into mice. RESULTS: The lipophilicity and affinity for sigma-1 receptor of (+)-[77Br]BrV-OH were lower than those of (+)-[77Br]pBrV. (+)-[77Br]BrV-OH also showed high tumor uptake in biodistribution experiments in DU-145 tumor-bearing mice,. Although (+)-[77Br]pBrV was retained in most tissues, (+)-[77Br]BrV-OH was cleared from these tissues. In blocking studies, the co-injection of SA4503 significantly decreased the tumor uptake of (+)-[77Br]BrV-OH. CONCLUSION: These results indicate that (+)-[76Br]BrV-OH has potential as a PET probe for sigma-1 receptor imaging.

Function of cytochrome P450 enzymes MycCI and MycG in Micromonospora griseorubida, a producer of the macrolide antibiotic mycinamicin.

The cytochrome P450 enzymes MycCI and MycG are encoded within the mycinamicin biosynthetic gene cluster and are involved in the biosynthesis of mycinamicin II (a 16-membered macrolide antibiotic produced by Micromonospora griseorubida). Based on recent enzymatic studies, MycCI is characterized as the C-21 methyl hydroxylase of mycinamicin VIII, while MycG is designated multifunctional P450, which catalyzes hydroxylation and also epoxidation at C-14 and C-12/13 on the macrolactone ring of mycinamicin. Here, we confirm the functions of MycCI and MycG in M. griseorubida. Protomycinolide IV and mycinamicin VIII accumulated in the culture broth of the mycCI disruption mutant; moreover, the mycCI gene fragment complemented the production of mycinamicin I and mycinamicin II, which are produced as major mycinamicins by the wild strain M. griseorubida A11725. The mycG disruption mutant did not produce mycinamicin I and mycinamicin II; however, mycinamicin IV accumulated in the culture broth. The mycG gene was located immediately downstream of the self-resistance gene myrB. The mycG gene under the control of mycGp complemented the production of mycinamicin I and mycinamicin II. Furthermore, the amount of mycinamicin II produced by the strain complemented with the mycG gene under the control of myrBp was approximately 2-fold higher than that produced by the wild strain. In M. griseorubida, MycG recognized mycinamicin IV, mycinamicin V, and also mycinamicin III as the substrates. Moreover, it catalyzed hydroxylation and also epoxidation at C-14 and C-12/13 on these intermediates. However, C-14 on mycinamicin I was not hydroxylated.